The present invention relates to inkjet printers, and particularly to memory on the heater chip of an inkjet printhead.
An inkjet printhead generally has a heater chip. The heater chip typically includes logic circuitry, a plurality of power transistors, and a set of heaters or resistors. A hardware or software printer driver will selectively address or energize the logic circuitry such that appropriate resistors are heated for printing. The memory is also used to identify the printhead to determine if the printhead is a monochrome printhead, a color printhead or a photograph quality printer printhead.
In the fuse configuration, the memory is an array of fuse memory elements. Each fuse memory element has a unique power transistor to enable writing or reading. This type of fuse memory has a constant memory density, for example, 140 bits per square millimeter. For example, a set of 13 fuses and programming transistors in an area 280 μm×340 μm (95200 μm2) yields 7323 μm2 per fuse, which is 137 fuses per 1,000,000 μm2 (or 1 mm2). Typical read currents are less than 5 mA; typical write or programming current is greater than 50 mA. Power transistors capable of generating the required programming current typically occupy a very large area per fuse. As a result, the number of memory elements is limited depending upon printhead size.